1. Field of the Invention
Apparatus and methods consistent with the present invention relate generally to low-power transmission in a wireless personal area network (WPAN), and more specifically to a low-power transmission in a WPAN for enhancing efficiency of a transmission energy in a contention period and a contention-free period and supporting quality of service (QoS).
2. Description of the Related Art
A WPAN implements an existing personal area network (PAN) by wireless connection. In contrast to a local area network (LAN) or a wide area network (WAN) being widely operated, the PAN is a network owned by an individual. Devices owned by the individual are interconnected to construct a network in order to provide convenience for the owner.
The Institute of Electrical and Electronics Engineers, Inc. (IEEE) 802.15 Working Group developed the WPAN for short distance wireless networks to standardize and implement the PAN. The IEEE 802.15 standard has four Task Groups. More particularly, IEEE 802.15.1 standardizes the well-known Bluetooth technology, whereas IEEE 802.15.3 standardizes the high rate WPAN. Additionally, IEEE 802.15.4 standardizes low rate WPAN.
The WPAN, which is a short distance wireless network, supports various portable computing devices including electronic devices such as a personal computer (PC), a personal digital assistant (PDA), a wireless printer, a storage medium, a mobile phone, a set-top box, and the like.
FIG. 1 depicts a structure of a superframe used for wireless communications under the WPAN environment.
In FIG. 1, the superframe consists of a beacon used as a sync signal, a contention access period (CAP) called a contention period, and a channel time allocation period (CTAP) being a contention-free period. The contention period conforms to the carrier sense multiple access with collision avoidance (CSMA/CA) protocol. In case of the IEEE 802.15.3, the time division multiple access (TDMA) technology is adopted in the contention-free period.
Under the WPAN environment, the devices generally have a limited energy source and thus its energy consumption is restricted. It can be said that a life span of the network depends on the energy consumption of the devices. Thus, a technology is demanded to enhance the efficiency of the transmission energy in the contention period and the contention-free period and to support quality of service (QoS).